1. Field of the Invention
The present invention relates to the field of magnetic bearings, and more specifically to the field of passive magnetic bearings.
2. Description of Related Art
In any spinning system, for example, a motor of a CD-ROM device or a motor of a heat-dissipating fan, the selection of a bearing is very important in order to maintain the stability and prolong the life of the spinning system. The key point in prolonging the life of the bearing lies in how to reduce the mechanical friction between the bearing and a spindle.
Conventional bearings can be divided into two main categories, that is, ball bearings and self-lubricating bearings. The self-lubricating bearings have the advantage of low price, but also have the disadvantage of short life. The ball bearings have the advantage of long life, but also have the disadvantage of high price and poor impact resistibility.
Therefore, in order to overcome the disadvantages of the traditional bearings, magnetic bearings have been invented. The magnetic bearings make use of magnetic force to suspend spinning components thereof, and thus have the advantages of being non-engaging and non-lubricating. Conventional magnetic bearings can be roughly divided into three categories and are presented as following:
Firstly, U.S. Pat. No. 5,545,937 discloses a spindle motor assembly including a magnetic bearing and a hydrodynamic bearing, wherein the magnetic bearing further including a pair of single pole magnetic rings complementary to each other. The advantage of the spindle motor is that it is convenient to assemble. The disadvantage is that the hydrodynamic bearing may still cause substantial mechanical friction and moreover the spindle motor includes radially-charged magnets which are not easy to produce.
Secondly, U.S. Pat. No. 5,619,083 discloses a passive magnetic bearing including a hydrodynamic bearing and a pair of multiple pole magnetic rings complementary to each other so that high stiffness is created. The advantage of the magnetic bearing is that it consists of axially-charged magnets which are convenient for mass production. However, the disadvantage again arises from the possible mechanical friction caused by the hydrodynamic bearing.
Thirdly, U.S. Pat. No. 4,340,260 discloses a magnetic suspension bearing having a unique configuration. The main advantage of the magnetic suspension bearing is that spacers are provided in air gaps and covers made of non-magnetic material served as dampers so that impact forces are absorbed and limited.
Therefore, the present invention intends to provide a magnetic bearing to overcome the mentioned disadvantages so as to be well received in the related industry.
It is the objective of the present invention to provide a magnetic bearing to minimize the mechanical friction between a spindle and a bearing so that life of the bearing is prolonged.
It is another objective of the present invention to provide a magnetic bearing such that the magnetic bearing is appropriately designed to prevent magnetic-flux-leakage, thereby creating a highly-efficient bearing.
It is a further objective of the present invention to provide a magnetic bearing that is easy to assemble so that cost and time related to the manufacturing of the magnetic bearing is low.
In accordance with these and other objectives of the invention, the magnetic bearing comprises a base, a spindle rotatably mounted onto the base and a magnetic portion mounted between the base and the spindle to provide a magnetic repulsion that suspends the spindle. A retaining portion is mounted on the base and between a tip end of the spindle and the base to support the spindle.